The invention relates to sampling and concentrative apparatus and methods for collection of trace analytes from surfaces and substrates where the analyte is in the form of a particulate or a vapor adherent to a particulate and particularly to such apparatus and methods as are useful in surveillance for trace explosives residues.
There is a need for inspection and sampling of persons, articles of clothing, buildings, furnishings, vehicles, baggage, cargo containers, dumpsters, packages, mail, and the like for contaminating residues (termed here more generally “trace analytes”) that may indicate chemical, radiological, biological, illicit, or infectious hazards. Applications involve detection of trace materials, both particles and optionally vapors, associated with persons who have handled explosives, detection of toxins in mail, or detection of spores on surfaces, while not limited thereto.
Current methods for surface sampling often involve contacting use of swabs or liquids, but methods for sampling by “sniffing” are preferred. To inspect mail or luggage for example, the sampling method of U.S. Pat. No. 6,887,710 involves first placing the article or articles in a box-like enclosure equipped with airlocks, directing a blast of air onto the exposed surfaces in order to dislodge particles associated with the articles, then sampling the gaseous contents of the box by drawing any resulting aerosol through a sampling port. However, the process is inherently slow because each article or person must be moved into the box or chamber and the box sealed before sampling, an obvious disadvantage when large numbers of articles or persons must be screened, or when the articles are larger than can be reasonably enclosed, such as a truck, shipping container, or the hallway surfaces of a building. Similar comments may be made regarding the teachings of U.S. Pat. No. 6,324,927 to Ornath, where an enclosed shaker is used to dislodge particles.
An approach for sampling persons is seen in U.S. Pat. No. 6,073,499 to Settles, aspects of which are also discussed in “Sniffers: fluid dynamic sampling for olfactory trace detection in nature and homeland security”, J Fluids Eng 127:189-218.
McGown in U.S. Pat. No. 4,909,090 describes a hand-held vapor sampler, optionally with a shroud for enclosing a sampling space, for using low pressure puffs of hot air to vaporize illicit substances on surfaces and trap any vapors on a collector coil. The coil contains ribbon-like windings of metal which have a thin coating of material such as an organic polymer effective in absorbing organic molecules such as cocaine. However, particles are not sampled and would not be successfully aspirated under the conditions described, which relies on a 250 Watt lamp and a spring-actuated plunger for generating a puff of air. Improvements to the collector/desorber device are disclosed in U.S. Pat. No. 5,123,274 to Carroll.
Ishikawa in U.S. Pat. No. 7,275,453 discloses a cover enclosure in contact with a surface, the enclosure with internally directed jet for operatively flushing and ejecting particles from the surface. The particles may be collected by means of an inertial impactor and thermally gasified from the impactor for detection of chemical constituents by mass spectroscopy. Use of a plate-type inertial impactor avoids the need for a fine-mesh filter, such as would become clogged.
Various particle and vapor traps are disclosed in patents to Linker of Sandia Labs, including U.S. RE38,797 and U.S. Pat. Nos. 7,299,711, 6,978,657, 6,604,406, 6,523,393, 6,345,545, 6,085,601 and 5,854,431, by Corrigan in U.S. Pat. Nos. 5,465,607 and 4,987,767, and Syage in U.S. Pat. No. 7,299,710, but implementation has proved difficult because particles have been found to poison commonly used vapor trap materials and means for efficiently separating particles and vapors are not recognized.
Teachings by Hitachi in U.S. Pat. No. 7,275,453 relate to an unusual inertial impactor with central void for discarding particles in excess of the cut size of the impactor. This has the unfortunate effect of dramatically reducing the amount of analyte available for detection. Also disclosed is a heatable rotary trap, as has longstandingly been used in the art.
Detection technologies are known. Of particular interest for detection of explosives are electron capture (often combined with gas chromatography), ion mobility spectroscopy, mass spectroscopy and chemiluminescence (often combined with gas chromatography).
One common analytical instrument for detection of nitrate-type explosives relies on pyrolysis followed by redox (electron capture) detection of NO2 groups (Scientrex EVD 3000), but is prone to false alarms. Also of interest is differential mobility spectroscopy as described in U.S. Pat. No. 7,605,367 to Miller. Ion mobility spectroscopic (IMS) detectors are in widespread use and typically have picogram sensitivity. IMS requires ionization of the sample, which is typically accomplished by a radioactive source such as Nickel-63 or Americium-241. This technology is found in most commercially available explosive detectors like the GE VaporTracer (GESecurity, Bradenton, Fla.), Sabre 4000 (Smiths Detection, Herts, UK), Barringer IonScan™ 400, and Russian built models.
The luminescence of certain compounds undergoing reaction with electron-rich explosive vapors has been improved with the introduction of amplifying fluorescent polymers as described in U.S. Pat. No. 7,208,122 to Swager (ICx Technologies, Arlington Va.). Typically vapors are introduced into a tubular sensor lined with a conductive quenchable fluorescent polymer by suction. These sensors lack a pre-concentrator and work only for analytes with electron-donating properties. More recent advances have extended work with fluorescent polymers to include boronic peroxide-induced fluorescence, as is useful for detecting certain classes of explosives.
Other analytical modalities are available, and include the MDS Sciex CONDOR, Thermedics EGIS, Ion Track Instruments Model 97, the Sandia Microhound, Smith's Detection Cyranose, FIDO® (FLIR Systems, Arlington Va., formerly ICx Technologies), Gelperin's e-nose (U.S. Pat. No. 5,675,070), Implant Sciences' Quantum Sniffer, and others. However, these technologies are associated with aspiration and analysis of vapors, which are typically in vanishingly small concentrations, either because a) the vapor pressure of the material is inherently small, or b) if vapor pressure is larger, then significant quantities of a more volatile analyte will have been lost due to ageing of the material prior to sampling. Some of these detectors also have had maintenance issues, often related to fouling due to aspiration of particles.
Aerodynamic focusing has been used to produce particle beams or ribbons in a gas stream, process in which the gas streamlines are separated into a particle-depleted sheath flow and a particle-enriched flow. The two flows can then be separated, resulting in particle concentration. An aerodynamic lens particle concentration system typically consists of four parts: a flow control orifice, at least one focusing lenses, an acceleration nozzle, and a skimmer. The choked inlet orifice fixes the mass flow rate through the system and reduces pressure from ambient to the value required to achieve aerodynamic focusing. The focusing lenses are a series of orifices contained in a tube that create a converging-diverging path resulting in flow accelerations and decelerations, through which particles are separated from the carrier gas due to their inertia and focused into a tight particle beam or ribbon. The accelerating nozzle controls the operating pressure within the lens assembly and accelerates particles to downstream destinations. The skimmer is typically a virtual impactor with virtual impactor void for collecting the particle beam or ribbon while diverting the greater mass of the particle-depleted bulk flow, thus concentrating the particle fraction.
Focusing of a range of micron and submicron size aerosol particles has been carried out using aerodynamic forces in periodic aerodynamic lens arrays [see Liu et al, 1995, Generating particle beams of controlled dimensions and divergence, Aerosol Sci. Techn., 22:293-313, Wang, X et al, 2005, A design tool for aerodynamic lens system, Aerosol Sci Techn 39:624-636; US Pat. Appl. Doc. 2006/0102837 to Wang]. Such arrays may be used as inlets to on-line single-particle analyzers [see Wexler and Johnston (2001) in Aerosol Measurement: Principles, Techniques, and Applications, Baron and Willeke eds, Wiley, New York, and U.S. Pat. No. 5,565,677 to Wexler]. As known in the art, a major class of skimmers generally comprise a cone or plate with a hole in the center (i.e., are virtual impactors).
Aerodynamic lenses have been used in particle mass spectrometers and as an adjunct to ion mobility spectroscopy, (for example as described in U.S. Pat. Nos. 7,256,396, 7,260,483, and 6,972,408 and more recently in US Pat. 2010/0252731), where high vacuum is used (0.1 to 30 mTorr). In this system, analyte vapors released from a very well collimated particle beam (typically <0.25 mm diameter) are laser ablated and ionized in flight and the resulting vapors are conveyed in a buffer gas at high vacuum, typically with Einzel lensing, to a mass spectrometer or an ion mobility spectrometer. The downstream analyzer can be badly damaged by the entry of intact particles. Moreover, the particle-by-particle approach taught in the art substantially limits application for high throughput analysis and is not scaleable except by an impractical redundancy of parallel systems.
Related systems are described in PCT Publication WO/2008/049038 to Prather, U.S. Pat. No. 6,906,322 to Berggren, and U.S. Pat. No. 6,664,550 to Rader. However, these devices are readily overloaded when confronted with large amounts of complex mixtures, interferents, and dust, such as are likely to be encountered in routine use.
Thus, strategies are needed to improve analyte collection efficiency and avoid interferences. There is a need for a front end device with directional head for mobilization of particles from substrate to aerosol, a head that can be portably directed to dislodge particles and optionally vapor residues from target surfaces, then efficiently capture and concentrate them before presentation to an analytical instrument of choice, an approach that optimizes sensitivity and can speed deployment because the need to enclose the target surface in a sealed chamber or shroud is overcome. In particular, there is a need for a front end collection system that may be used in environments where a small amount of a target analyte must be detected in the presence of larger amounts of ubiquitous background particulates, for example dust and water with small amounts of target analyte, and with means for regenerating capture surfaces.
The preferred devices, systems and methods overcome the above disadvantages and limitations and are useful in detecting hazardous particles, vapors and volatiles associated with objects, structures, surfaces, cavities, vehicles or persons.